Evaporation of heated droplets at different wetting modes: A decoupled study of diffusive and convective effects

Abstract

The evaporation of water droplets on the heated substrate exhibits diverse wetting modes such as Constant Contact Angle (CCA) mode, Constant Contact Radius (CCR) mode, and mixed mode. Coupled with multiple driving forces of vapor mass transfer, these wetting modes, especially mixed mode, have complex but unclear effects on droplet evaporation. The present study uses moving-mesh numerical simulation based on Arbitrary Lagrangian-Eulerian method to realize the evaporation of droplets at different wetting modes, and the simulation results of mixed mode evaporation agree well with experiments. The variations of temperature field during droplet evaporation are investigated, and the resemblance among diverse wetting modes can be attributed to the shape and the fluid flow intensity of the droplet. Decoupled analyses are conducted on the two major driving forces of evaporation for heated droplets at different wetting modes: diffusion and convection, and the effect of internal and external flows on the distribution of multiple mass fluxes along the droplet surface is elucidated. During droplet evaporation, CCR mode is more dependent on the diffusive effect, CCA mode is more dependent on the convective effect, and mixed mode lies in between. The present study elucidates the effect of wetting modes on the variation of multiple physical fields for the evaporation of heated droplets, promising in industrial and technological fields such as thermal management, droplet microfluidics, and medical treatment.